Many synthetic polymers, both elastomers and thermoplastics, are produced by solution or slurry polymerization techniques, so that the polymers are initially obtained as solutions or slurries in solvents/diluents. The recovery of the solid polymer from solution or slurry conventionally involves a series of process steps, each of which requires a significant input of energy. Normally, a steam stripping procedure is adopted, in which the polymer solution or slurry is contacted with steam to flash off the solvent or diluent The bulk of the added water is drained off the polymer. The polymer is then dried, e.g. by warming and sometimes by use of dewatering and drying extruders, to recover the solid polymer crumb in relatively dry, solvent free form.
Attempts have been made in the past to effect polymer recovery from solutions or slurries in organic solvents or diluents without the use of water, in order to eliminate the water removal steps. Such attempts have centered around the use of an extruder, to effect removal of the solvent by volatilization thereof. In order for such an extrusion process to be successful, the polymer solution must be concentrated, e.g. to about 50% polymer content, to provide a composition of sufficient viscosity for the extruder to efficiently impart energy to it. Such preconcentration is difficult to achieve. It must be done by heating the solution or slurry under carefully controlled conditions to avoid combustion and polymer degradation. The viscosity of polymer solutions increases with increasing polymer concentration, so that the heat transfer requirements of heating apparatus to be used in preconcentration are very demanding. Also, the polymer tends to adhere to the heat transfer surfaces, causing plugging of the equipment, unless the heat transfer surface is continuously wiped, which is difficult to achieve.
It is an object of the present invention to provide a novel process for concentration of polymer in a solution or slurry thereof in a solvent or diluent.
It is a further object of the invention to provide such a process which is comparatively low in its energy requirements.
It is a further object of the invention to provide a novel process for the concentration of polymer in a solution or slurry thereof and for the recovery of the polymer essentially free of solvent or diluent.